8-speed transmission

ABSTRACT

The transmission has a plurality of members that can be utilized in powertrains to provide eight forward speed ratios and one reverse speed ratio. The transmission includes three planetary gear sets, six torque-transmitting devices, a split sun gear, two fixed interconnections and a grounded member. The powertrain includes an engine and torque converter that is continuously connected to one of the planetary gear members and an output member that is continuously connected with another one of the planetary gear members. The six torque-transmitting devices provide interconnections between various gear members, and the transmission housing, and are operated in combinations of two to establish eight forward speed ratios and one reverse speed ratio.

TECHNICAL FIELD

The present invention relates to a power transmission having three planetary gear sets that are controlled by six torque-transmitting devices to provide eight forward speed ratios and one reverse speed ratio.

BACKGROUND OF THE INVENTION

Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission, and a differential or final drive. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times. The number of forward speed ratios that are available in the transmission determines the number of times the engine torque range is repeated. Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point during cruising, other than the most efficient point. Therefore, manually-shifted (countershaft transmissions) were the most popular.

With the advent of three- and four-speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improved the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration.

Six-speed transmissions offer several advantages over four- and five-speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ power transmissions having six or more forward speed ratios, passenger cars are still manufactured with three- and four-speed automatic transmissions and relatively few five or six-speed devices due to the size and complexity of these transmissions.

Seven-, eight- and nine-speed transmissions provide further improvements in acceleration and fuel economy over six-speed transmissions. However, like the six-speed transmissions discussed above, the development of seven-, eight- and nine-speed transmissions has been precluded because of complexity, size and cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved transmission having three planetary gear sets controlled to provide eight forward speed ratios and one reverse speed ratio.

The transmission family of the present invention has three planetary gear sets, each of which includes a first, second and third member, which members may comprise a sun gear, a ring gear, or a planet carrier assembly member, in any order. One member of one of the planetary gear sets is split into two portions.

In referring to the first, second and third gear sets in this description and in the claims, these sets may be counted “first” to “third” in any order in the drawing (i.e., left to right, right to left, etc.). Additionally, the first, second or third members of each gear set may be counted “first” to “third” in any order in the drawing (i.e., top to bottom, bottom to top, etc.) for each gear set.

Each carrier member can be either a single-pinion carrier member (simple) or a double-pinion carrier member (compound). Embodiments with long pinions are also possible.

One planetary gear set has a split first member consisting of a first portion and a second portion, which enables a connection to the second member of the planetary gear set between the first and second portions of the split first member.

A first interconnecting member continuously connects the second member of the first planetary gear set with the third member of the second planetary gear set.

A second interconnecting member continuously connects the first member of the first planetary gear set with the first member of the third planetary gear set.

The third member of the first planetary gear set is continuously connected to a stationary member (transmission housing/casing). The input member is continuously connected with the first portion of the split first member of the second planetary gear set. The output member is continuously connected with the third member of the third planetary gear set.

A first torque-transmitting device, such a brake, selectively connects the second member of the third planetary gear set with a stationary member (transmission housing/casing).

A second torque-transmitting device, such as a brake, selectively connects the first member of the first planetary gear set with a stationary member (transmission housing/casing).

A third torque-transmitting device, such as a clutch, selectively connects the first member of the first planetary gear set with the second member of the second planetary gear set.

A fourth torque-transmitting device, such as a clutch, selectively connects the first member of the first planetary gear set with the second portion of the split first member of the second planetary gear set.

A fifth torque-transmitting device, such as a clutch, selectively connects the second member of the second planetary gear set with the third member of the third planetary gear set.

A sixth torque-transmitting device, such as a clutch, selectively connects the second portion of the split first member of the second planetary gear set with the second member of the third planetary gear set.

The six torque-transmitting devices are selectively engageable in combinations of two to yield eight forward speed ratios and one reverse speed ratio.

A variety of speed ratios and ratio spreads can be realized by suitably selecting the tooth ratios of the planetary gear sets.

The above features and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 a is a schematic representation of a powertrain including a planetary transmission in accordance with the present invention;

FIG. 1 b is a truth table and chart depicting some of the operating characteristics of the powertrain shown in FIG. 1 a; and

FIG. 1 c is a schematic representation of the powertrain of FIG. I a depicted in lever diagram form.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, there is shown in FIG. 1 a a powertrain 10 having a conventional engine and torque converter 12, a planetary transmission 14, and a conventional final drive mechanism 16. The engine 12 may be powered using various types of fuel to improve the efficiency and fuel economy of a particular application. Such fuels may include, for example, gasoline; diesel; ethanol; dimethyl ether; etc.

The planetary transmission 14 includes an input member 17 continuously connected with the engine 12, a planetary gear arrangement 18, and an output member 19 continuously connected with the final drive mechanism 16. The planetary gear arrangement 18 includes three planetary gear sets 20, 30 and 40.

The planetary gear set 20 includes a sun gear member 22, a ring gear member 24, and a planet carrier assembly member 26. The planet carrier assembly member 26 includes a plurality of pinion gears 27 rotatably mounted on a carrier member 29 and disposed in meshing relationship with both the sun gear member 22 and the ring gear member 24.

The planetary gear set 30 includes first and second split sun gear member portions 320, 321, a ring gear member 34, and a planet carrier assembly member 36. The planet carrier assembly member 36 includes a plurality of pinion gears 37 rotatably mounted on a carrier member 39 and disposed in meshing relationship between the first and second split sun gear member portions 320, 321 and the ring gear member 34.

The planetary gear set 40 includes a sun gear member 42, a ring gear member 44, and a planet carrier assembly member 46. The planet carrier assembly member 46 includes a plurality of pinion gears 47 mounted on a carrier member 49 and disposed in meshing relationship with both the ring gear member 44 and the sun gear member 42.

The planetary gear arrangement also includes six torque-transmitting devices 50, 52, 54, 55, 56 and 57. The torque-transmitting devices 50 and 52 are stationary-type torque-transmitting devices, commonly termed brakes or reaction clutches. The torque-transmitting devices 54, 55, 56 and 57 are rotating-type torque-transmitting devices, commonly termed clutches.

The input member 17 is continuously connected with the split sun gear member portion 320 of the planetary gear set 30. The output member 19 is continuously connected with the ring gear member 44 of the planetary gear set 40. The ring gear member 24 is continuously connected with the transmission housing 60.

A first interconnecting member 70 continuously connects the planet carrier assembly member 26 with the ring gear member 34. A second interconnecting member 72 continuously connects the sun gear member 22 with the sun gear member 42.

A first torque-transmitting device, such as brake 50, selectively connects the planet carrier assembly member 46 with the transmission housing 60. A second torque-transmitting device, such as brake 52, selectively connects the sun gear member 22 and the sun gear member 42 via interconnecting member 72 with the transmission housing 60. A third torque-transmitting device, such as clutch 54, selectively connects the sun gear member 22 with the planet carrier assembly member 36. A fourth torque-transmitting device, such as clutch 55, selectively connects the sun gear member 22 with the split sun gear member portion 321. A fifth torque-transmitting device, such as clutch 56, selectively connects the planet carrier assembly member 36 with the ring gear member 44. A sixth torque-transmitting device, such as clutch 57, selectively connects the sun gear member 321 with the planet carrier assembly member 46.

As shown in FIG. 1 b, and in particular the truth table disclosed therein, the torque-transmitting devices are selectively engaged in combinations of two to provide eight forward speed ratios and one reverse speed ratio, all with single transition shifts and with a double overdrive.

As set forth above, the engagement schedule for the torque-transmitting devices is shown in the truth table of FIG. 1 b. The chart of FIG. 1 b describes the ratio steps that are attained in the above described transmission. For example, the step ratio between the first and second forward speed ratios is 1.61, while the step ratio between the reverse speed ratio and first forward ratio is −0.60.

Referring to FIG. 1 c, the embodiment of powertrain 10 depicted in FIG. 1 a is illustrated in a lever diagram format.

The powertrain 10 includes an input member 17, an output member 19, a first planetary gear set 20A having three nodes: a first node 22A, a second node 26A and a third node 24A; a second planetary gear set 30A having three nodes: a first node 32A (corresponding with elements 320 and 321 of FIG. 1 a), a second node 36A and a third node 34A; a third planetary gear set 40A having three nodes: a first node 42A, a second node 46A and a third node 44A.

The input member 17 is continuously connected with the node 32A. The output member 19 is continuously connected with the node 44A. The node 24A is continuously connected with the transmission housing 60.

The node 26A is continuously connected with the node 34A via interconnecting member 70. The node 22A is continuously connected with node 42A via interconnecting member 72.

A first torque-transmitting device, such as brake 50 engages the node 46A with the transmission housing 60. A second torque-transmitting device, such as brake 52, engages the nodes 22A and 42A via interconnecting member 72 with the transmission housing 60. A third torque-transmitting device, such as clutch 54, engages the nodes 22A and 42A via interconnecting member 72 with the node 36A. A fourth torque-transmitting device, such as clutch 55, engages the nodes 22A and 42A via interconnecting member 72 with the node 32A. A fifth torque-transmitting device, such as clutch 56, engages the node 36A with the node 44A. A sixth torque-transmitting device, such as clutch 57, engages the node 32A with the node 46A.

To establish ratios, two torque-transmitting devices are engaged for each gear state. The engaged torque-transmitting devices are represented by an “X” in each respective row of FIG. 1 b. For example, to establish reverse gear, the brake 50 and clutch 55 are engaged. The brake 50 engages the node 46A with the transmission housing 60. The clutch 55 engages the nodes 22A and 42A with the node 32A. Likewise, the eight forward ratios are achieved through different combinations of clutch engagement as per FIG. 1 c.

The powertrain 10 may share components with a hybrid vehicle, and such a combination may be operable in a “charge-depleting mode”. For purposes of the present invention, a “charge-depleting mode” is a mode wherein the vehicle is powered primarily by an electric motor/generator such that a battery is depleted or nearly depleted when the vehicle reaches its destination. In other words, during the charge-depleting mode, the engine 12 is only operated to the extent necessary to ensure that the battery is not depleted before the destination is reached. A conventional hybrid vehicle operates in a “charge-sustaining mode”, wherein if the battery charge level drops below a predetermined level (e.g., 25%) the engine is automatically run to recharge the battery. Therefore, by operating in a charge-depleting mode, the hybrid vehicle can conserve some or all of the fuel that would otherwise be expended to maintain the 25% battery charge level in a conventional hybrid vehicle. It should be appreciated that a hybrid vehicle powertrain is preferably only operated in the charge-depleting mode if the battery can be recharged after the destination is reached by plugging it into an energy source.

While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims. 

1. A multi-speed transmission comprising: an input member; an output member; first, second and third planetary gear sets each having first, second and third members and wherein the first member of one of said planetary gear sets is split into first and second portions; a first interconnecting member continuously connecting said second member of said first planetary gear set with said third member of said second planetary gear set; a second interconnecting member continuously connecting said first member of said first planetary gear set with said first member of said third planetary gear set; said third member of said first planetary gear set being continuously connected with a stationary member; and six torque-transmitting devices, wherein each of said six torque-transmitting devices selectively interconnects said members of said planetary gear sets with said stationary member or with other members of said planetary gear sets, said six torque-transmitting devices being engaged in combinations of two to establish at least eight forward speed ratios and at least one reverse speed ratio between said input member and said output member.
 2. The transmission of claim 1, wherein a first of said six torque-transmitting devices is operable for selectively connecting said second member of said third planetary gear set with said stationary member.
 3. The transmission of claim 2, wherein a second of said six torque-transmitting devices is operable for selectively connecting said first member of said first planetary gear set with said stationary member.
 4. The transmission of claim 3, wherein a third of said six torque-transmitting devices is operable for selectively connecting said first member of said first planetary gear set with said second member of said second planetary gear set.
 5. The transmission of claim 4, wherein the first member of said one of said planetary gear sets is the first member of said second planetary gear set, and wherein a fourth of said six torque-transmitting devices is operable for selectively connecting said first member of said first planetary gear set with said second portion of said first member of said second planetary gear set.
 6. The transmission of claim 5, wherein a fifth of said six torque-transmitting devices is operable for selectively connecting said second member of said second planetary gear set with said third member of said third planetary gear set.
 7. The transmission of claim 6, wherein a sixth of said six torque-transmitting devices is operable for selectively connecting said second portion of said first member of said second planetary gear set with said second member of said third planetary gear set.
 8. The transmission defined in claim 1, wherein said first and second torque-transmitting devices comprises brakes, and said third, fourth, fifth and sixth torque-transmitting devices comprise clutches.
 9. The transmission of claim 1, wherein said first, second and third members of said first, second and third planetary gear sets comprise a sun gear member, a planet carrier assembly member and a ring gear member, respectively.
 10. The transmission of claim 1, wherein the first member of said one of said planetary gear sets is the first member of said second planetary gear set, and wherein said input member is continuously connected with said first portion of said first member of said second planetary gear set; and said output member is continuously connected with said third member of said third planetary gear set.
 11. The transmission of claim 1, wherein a connection to one of said torque-transmitting devices extends between said first and second portions of said split first member.
 12. A multi-speed transmission comprising: an input member; an output member; first, second and third planetary gear sets each having first, second and third members and wherein the first member of said second planetary gear set is split into first and second portions thereby allowing said second member of said one of said planetary gear sets to be selectively connected to other members of said one planetary gear sets between said first and second portions; said input member being continuously connected with said first portion of said first member of said second planetary gear set; said output member being continuously connected with said third member of said third planetary gear set; a first interconnecting member continuously connecting said second member of said first planetary gear set with said third member of said second planetary gear set; a second interconnecting member continuously connecting said first member of said first planetary gear set with said first member of said third planetary gear set; said third member of said first planetary gear set being continuously connected with a stationary member; a first torque-transmitting device selectively connecting said second member of said third planetary gear set with said stationary member; a second torque-transmitting device selectively connecting said first member of said first planetary gear set with said stationary member; a third torque-transmitting device selectively connecting said first member of said first planetary gear set with said second member of said second planetary gear set; a fourth torque-transmitting device selectively connecting said first member of said first planetary gear set with said second portion of said first member of said second planetary gear set; a fifth torque-transmitting device selectively connecting said second member of said second planetary gear set with said third member of said third planetary gear set; a sixth torque-transmitting device selectively connecting said first member of said second planetary gear set with said second member of said third planetary gear set; and said six torque-transmitting devices being engaged in combinations of two to establish at least eight forward speed ratios and at least one reverse speed ratio between said input member and said output member.
 13. The transmission of claim 12, wherein said first, second and third members of said first, second and third planetary gear sets comprise a sun gear member, a planet carrier assembly member and a ring gear member, respectively.
 14. A multi-speed transmission comprising: an input member; an output member; first, second and third planetary gear sets each having a sun gear member, planet carrier assembly member and ring gear member and wherein the sun gear member of said second planetary gear set is split into first and second portions thereby allowing said planet carrier assembly member of said second planetary gear set to be selectively connected to other members of said planetary gear sets between said first and second portions; said input member being continuously interconnected with said first portion of said sun gear member of said second planetary gear set; said output member being continuously interconnected with said ring gear member of said third planetary gear set; said ring gear member of said first planetary gear set being continuously connected with a stationary member; a first interconnecting member continuously connecting said planet carrier assembly member of said first planetary gear set with said ring gear member of said second planetary gear set; a second interconnecting member continuously connecting said sun gear member of said first planetary gear set with said sun gear member of said third planetary gear set; a first torque-transmitting device selectively connecting said planet carrier assembly member of said third planetary gear set with said stationary member; a second torque-transmitting device selectively connecting said sun gear member of said first planetary gear set with said stationary member; a third torque-transmitting device selectively connecting said sun gear member of said first planetary gear set with said planet carrier assembly member of said second planetary gear set; a fourth torque-transmitting device selectively connecting said sun gear member of said first planetary gear set with said second portion of said sun gear member of said second planetary gear set; a fifth torque-transmitting device selectively connecting said planet carrier assembly member of said second planetary gear set with said ring gear member of said third planetary gear set; a sixth torque-transmitting device selectively connecting said second portion of said sun gear member of said second planetary gear set with said planet carrier assembly member of said third planetary gear set; said six torque-transmitting devices being engaged in combinations of two to establish eight forward speed ratios and one reverse speed ratio between said input member and said output member. 